Embedded servo fields are recorded on disc surfaces and are used by a servo controller in accurately aligning a read/write head over a desired track. There are imperfections in the processes of positioning the embedded servo fields on a disc surface and, in general, the position of each embedded servo field has a repeatable runout error. During disc drive manufacture, the positions of the embedded servo fields is measured. A correction or compensation table is then calculated. The compensation table is stored in the disc drive.
During subsequent normal operation of the disc drive by the user, the correction or compensation table is used by the servo control loop to improve the alignment of the head over a selected data track.
Due to the presence of noise of various kinds, there are imperfections in the process of measuring the positions of the embedded servo fields. Multiple iterations of each measurement are needed to overcome the noise problems and accurately calculate a compensation table. The measurement process becomes increasingly time consuming as the number of tracks on a disc increases in newer disc drive designs. The time consumed in making multiple iterations of measurements is a barrier to economical, rapid mass production of disc drives.
A method and apparatus are needed to reduce the number of iterations of measurements and reduce the time needed to measure repeatable run out errors and calculate a compensation table.